#Edison must inspect even more of its #Long_Beach power grid

….Most of the city and the remainder of Edison’s 50,000-square-mile service area has what the company calls a radial design, where outages can be isolated along system branches. The August power outages occurred in this part of the system.

Downtown Long Beach’s power system downtown is what Edison calls a networked system, with every circuit connected to every other circuit. Similar systems operate in New York and Chicago. It has the advantage that when power fails in one part of the network, current can flow in from another part of the network.

But that same interconnectivity creates the disadvantage seen in Long Beach in July, when a failed cable splice caught fire and exploded in an underground vault. Fire from one vault spread via underground conduits to other vaults, causing several to explode.

In some cases, vault covers were hurtled skyward in the blasts. One vault cover that flew off July 30 damaged the side of an apartment building. Power to about 30,000 customers had to be cut to restore the system during those outages.

Ferree said Edison has made changes in the downtown system, adding additional cables to increase the capacity of the power grid. It also added additional pathways for the power to flow between potential trouble spots. The company had already begun the work of tethering the downtown manhole covers — now it appears it will have to expand that work to a wider territory.

In contrast, the Los Angeles Department of Water and Power has been adding tethers to its underground vaults for the past several years. However, it will still be several years before that large job is completed.

And on top of the PUC scrutiny, Edison executives face questioning by the Long Beach City Council on Tuesday.